Indented circles on roads

This is probably too much of a nerdy engineering question for you, but what the heck are those indented circles in the road on many hills in Japan? I hope you know what I mean because I’m not sure how to describe them. Road rings? Doughnut depressions? I’m guessing they are there to provide improved traction, but I’ve never seen a road surface like this anywhere outside of Japan. Is there something about conditions here that demand them?

Stan W., Kobe

Dear Stan,

I have a soft spot in my heart for nerdy engineers, and I’ve wondered myself about those circles, so I was more than happy to take up your question. My investigation led me, after a couple of wrong turns, to Nagato Abe, an engineer with Toa Road Corporation and a member of the Committee on Pavement Engineering over at the Japanese Society of Civil Engineers.

First of all, your hunch was correct: the circular indentations, which are called O-gata suberidome (O-shaped antislip grooves), are there to provide improved traction on hills, particularly when the road is wet. Japanese law requires some kind of antislip surface on roads built on grades of 7 percent or steeper, Abe explained, and the circles are one of the more common ways of meeting the requirement.

A company called Taiheiyo Precast Concrete Industry developed the technique in the 1950s, and although the patent has expired they still have the circle market pretty much cornered. Many construction companies have Taiheiyo come in just to do the circles-in-concrete on their projects. This road surface is particularly popular for the ramps in underground parking lots, shopping centers and other slopes in spaces too narrow to accommodate large, heavy equipment.

Abe showed me photos of how it’s done. After a section of concrete is poured in the usual way, a board is laid across the surface. A worker walks along the board setting rubber rings by hand into the wet concrete. Then a mat attached to a vacuum is laid over the entire surface to suck excess water out of the concrete. This concrete-vacuum process dries the concrete before it has a chance to run downhill, and it greatly shortens the time the road is off-limits to traffic. After about 30 minutes, the mat is moved to the next section and the rings are removed. There is no special significance to the circle shape. Taiheiyo tried squares at first, but rings proved easier to pull from the semi-dry concrete.

By the time the rings are out, the concrete has set enough that pedestrians and even bicycles can go across without damaging the surface. It’s ready for cars after about three hours. This is a big advantage in congested Japanese cities.

How well do the circles work? The Public Works Research Institute in Tsukuba, Ibaraki Prefecture, found that the indentations improve traction by about 15 percent. Traffic accidents on hills have declined 80 percent since the requirement for antislip measures was enacted in the ’60s.

You asked whether there was anything specific to Japan that would explain why the O-shaped grooves were developed here. Well, consider that Japan has only 378,000 sq. km of land, 70 percent of which is mountainous. By necessity, and for access to the sea, much of the country’s development has been on the coasts, even where the mountains come right down to the sea.

Add to this that Japan is a country subject to torrential rain, and you can understand that it has one heck of a lot of steep roads that would get treacherous in heavy rains if it weren’t for the antislip surfaces.

There are some interesting things happening in Japan in the field of road- surface engineering, according to Abe, particularly in the development of environmentally friendly pavements.

That bottle of wine you polished off at dinner may end up under your car wheels: recycled glass is ground into smooth pellets and mixed with polymers to create an antislip pavement. The glass content also makes the pavement colorful and reflective, alerting drivers to upcoming intersections and curves. In some cases, the use of such pavement eliminates the need for unsightly warning signs along the road.

New technologies may also help keep cities cooler in summer by reducing the surface heat of roads. One way this can be done is by incorporating reflective pigment and fine ceramic particles in the surface of the road to reflect the heat of the sun. Another way is to use water-retentive pavements — the pavement sucks up water on rainy days; later, on hot days, the road is cooled as the water evaporates in the sun. In tests, the temperature of such pavements was 10 to 14 C lower than conventional road surfaces.

Japan is also developing permeable pavement to reduce the runoff of rainwater from road surfaces, thus reducing the risk of floods, and it leads the world in reuse of asphalt mixtures — 99 percent of the asphalt torn up is recycled into new roads or repairs.

One intriguing idea, still in development, is a road surface that incorporates titanium oxide, which is a photo catalyst that can oxidize the toxic nitrogen oxides in automobile emissions and convert them into harmless nitrate ions.

In last month’s column about the Automated External Defibrillator (AED), I asked readers if they knew of opportunities to get trained on the AED in Japan in languages other that Japanese. I didn’t get any response on that — I smell an opportunity for help organizations — but Michael B. sent in this link for a manual, in reasonable English, for one of the AEDs used in Japan. It’s worth a look. www.adm.u-tokyo.ac.jp/office/anzeneisei/data/aed_manual_english.pdf